In some cases, an RF reader operates in a dense reader environment, i.e., an area with many readers sharing fewer channels than the number of readers. Each RF reader works to scan its interrogation zone for transponders, reading them when they are found. Because the transponder uses radar cross section (RCS) modulation to backscatter information to the readers, the RFID communications link can be very asymmetric. The readers typically transmit around 1 watt, while only about 0.1 milliwatt or less gets reflected back from the transponder. After propagation losses from the transponder to the reader the receive signal power at the reader can be 1 nanowatt for fully passive transponders, and as low as 1 picowatt for battery assisted transponders. When a low-power signal of narrow frequency bandwidth is received by an RF reader, the signal to noise ratio of the received signal may be very small.